Of the States within it, Cape Colony first claims consideration. In the central section the step or terrace formation is so marked, and the flats, which intervene between the rises, are of such extent, and of a nature so curious, that they form one of the most remarkable features of South Africa. They are known as "the Karroos," vast plains stretching northward, firstly as the Little Karroo from the lower coast ranges to the more elevated Zwarte Bergen, thence as the Great Karroo to the still loftier Nieuwveld Mountains. In the rainless season they present an aspect indescribably desolate, and at the same time a formidable military obstacle to any invasion of Cape Colony on a large scale from the north. They are then mere wastes of sand and dead scrub, lifeless and waterless. The first fall of rain produces a transformation as rapid as any effected by nature. The vegetable life of the Karroos, which has only been suspended, not extinguished, is then released; the arid watercourses are filled in a few hours, and the great desert tract becomes within that brief time a garden of flowers. Even then, from the scarcity of buildings and inhabitants, and hence of supplies, the Karroos still form a barrier not to be lightly attempted, unless by an army fully equipped, and carrying its own magazines; or, on the other hand, by a band of partisans so insignificant as to be able to subsist on the scanty resources available, and to disappear when these are exhausted, or the enemy approaches in strength. [Sidenote: Hills above Karroos.]